There are many industrial applications where it is necessary to cement glass bodies, particularly glass panes, to other materials. In many applications, this cementing must be durable and must withstand considerable mechanical stresses, as well as stresses imposed by atmospheric influences such as water, surrounding temperatures, sunlight, etc., for long periods of time.
Durable adhesive connections between glass bodies and other materials are useful in a number of applications such as facade glazing, and anchoring glass panes or laminated glass panes to window frames. Particularly rigorous standards must be met in the vehicle industries where durable cementing of glass panes to corresponding body parts is required; e.g., adhesion of windshields, and rear and side windows which cannot be opened. The requirements associated with windshields are particularly strict because the corresponding point of adhesion must withstand great mechanical stresses in the event of impact.
In many applications it is desirable to produce an effective connection between a glass body and another material by cementation because the connection can provide improved watertightness. Furthermore, in vehicle construction cemented panes contribute substantially to the torsional strength since a passenger compartment with a cemented panes is less vulnerable to torsional forces than passenger compartments where the panes have not been cemented. In addition, when glass panes have been cemented there is increased soundproofing or noise reduction, and weight reduction.
In cementing a vehicle pane, the cement will be applied either to the glass pane or a flange on the vehicle, and the pane will be brought into the proper position by application of pressure. When the pane is precisely positioned, it is necessary to use range spacers which prevent the thickness of the adhesive layer from being uneven. Such a procedure is described in the French document FR-A2 266 669. In that case, both bodies to be connected preferably have a cylindrical shape and are pressed together in such a way that an intermediate space is created between the surfaces. The space is closed off by two torus-shaped elastic sealing rings. The rings are fixed using two grooves that are embedded in the surface of the metal body. Two opposite openings in the metal body make it possible to completely fill the delimited space with liquid cement. Cementing a windshield of safety glass to a vehicle frame is also described in U.S. Pat. No. 4,551,372. In the process described therein, the inserted pane of safety glass has at least two glass layers that are connected together by a plastic layer. The outer glass layer of safety glass projects beyond the glass layer of safety glass facing the vehicle interior in a manner such that the edge area of the windshield is structured in steps. The cement which is used to cement the windshield is so flowable that it seals the stepped area and prevents penetration of humidity into the intermediate plastic layer of the safety glass. In accordance with one type of construction, air- and water-tightness of the stepped edge area is achieved by an adhesive mixture that can be hardened and, is available in a completely hardened state; i.e., no longer adhesive at the time of cementing the vehicle pane. This edge made of the hardened adhesive is accordingly provided with a groove-shaped recess into which a further adhesive is then introduced. The additional adhesive must be compatible with the already completely hardened adhesive.
The aforementioned procedure of anchoring a vehicle pane with an already hardened, no longer adhesive layer of a first adhesive and then introducing a second adhesive, which is still adhesive at the glazing process, is described in greater detail in U.S. Pat. No. 4,571,278 and in German Patent No. 3,409,960. This procedure is often referred as flush-glazing, and represents a further development of direct glazing by direct application of a adhesive cement to the glass pane or to the vehicle flange (direct glazing is likewise referred to as direct glazing). In flush-glazing, the profile of the cement already hardened at the time of cementing acts as a range spacer. Positioning the pane during installation is substantially simplified by this process. In fact, a few vehicle manufactures have already begun the standard installation of windshields and rear windows by flush-glazing, or will begin by the first part of 1991.
As described in German Patent No. 3,409,960 and U.S. Pat. No. 4,571,278, in flush-glazing the cement which adheres at the time of cementing is not brought into direct contact with the glass pane, but is applied directly to the edge area of the glass body or the profile of solidifiable cement, via an intermediate layer of a primer. After the primer has completely hardened and is solidified, a second cement is applied to it, preferably in the form of a profile that is inserted into a groove-shaped recess of the profile of the first cement. There is, however, a problem of intermediate adhesion between the two different cements. Therefore, the initial hardened cement strand should be either chemically or mechanically reactivated before applying the second cement strand. The contact surface between the two cement strands can also be enlarged by corrugation.
Although the adhesion problems of the second, still adhesive cement to the first, already hardened cement, can be addressed by chemical reactivation or mechanical reactivation of the profile surface of the hardened cement, these reactivations are not industrially practical solutions. The quality and extent of the reactivation cannot be controlled. Furthermore, a new work-place would be required for the reactivation stage; an undesirable additional cost.
Accordingly, the general object of the present invention is to eliminate the problems relating to adhesion of a second cement profile, still having adhesive characteristics at the time of cementing, to the first already hardened, cement profile.